Wrong. The original ARs were chambered in what was, at the time, the most popular centerfire varmint round, the .222 Remington. The military decided they wanted more power, so the .222 was lengthened, and eventually named .223 Remington so it wouldn't be confused with the .222.
Anyway, varmint bullets are designed to expand immediately upon impact. It used to be that this was accomplished by using very thin jackets on light bullets with high velocity, and that still works. But recent development has given us better bullets, such as the V-Max, which is basically a hollowpoint with a plastic tip in side it, which forces the hollowpoint to expand immediately on impact.
But... the military uses FMJ rounds, so as to not anger other countries (even though we never signed the Hague convention, we follow those rules). So a 55gr FMJ bullet was originally used. It was not *designed* to be an expanding or fragmenting bullet; that was just a happy accident. But it certainly isn't any more "friendly" than, say, a .308, if you get shot by one.
That old myth that we "shoot to wound" is crap, as is the argument of taking 1-2 people out of the fight to care for the wounded. Even today, when our military shoots, it shoots to kill, and the US is one of the few countries who bothers much about the wounded. Most of the countries we have or likely would fight just let them lay there.
-Troy